Modern analytical instruments, such as are used routinely in analytics, forensics, microbiology and clinical diagnostics, are able to carry out multiple detection reactions and analyses with multiple samples. In order to be able to carry out automated multiple investigations, diverse automatically operating devices for the spatial transfer of measuring cuvettes, reaction containers and reagent liquid containers are required, such as transfer arms with grip function, conveyor belts or rotatable transport wheels, and also devices for the transfer of liquids such as pipetting devices. The instruments include a central control unit which, by means of appropriate software, is able to plan and execute the working steps for the desired analyses largely independently.
Many of the analytical methods used in such automated analytical instruments are based on optical methods. Particularly widespread are measuring systems which depend on photometric (e.g., turbidimetric, nephelometric, fluorometric or luminometric) or radiometric measuring principles. These methods enable the qualitative and quantitative detection of analytes in liquid samples without having to provide additional separation steps. The determination of clinically relevant parameters, such as the concentration or activity of an analyte, is carried out repeatedly by mixing an aliquot of a body fluid from a patient, simultaneously or sequentially, with one or more test reagents in a reaction vessel, whereby a biochemical reaction is initiated which effects a measurable change to an optical property of the test mixture.
The measurement result is in turn transmitted by the measuring system to a memory unit and evaluated. The analytical instrument subsequently delivers sample-specific data to a user via an output medium such as a monitor, a printer or a network connection.
The measuring cuvettes, in which the test mixtures are provided, transported and finally analyzed with the aid of an optical measurement method, are, in the simplest case, in the form of single units and typically consist of transparent plastic. The measuring cuvettes are generally disposable, that is they are provided as single-use articles, so that cleaning and the contamination risk linked thereto can be eliminated. However, the highest demands are placed on the quality of the measuring cuvettes, since even the smallest fluctuations, for example in the wall thickness, the diameter, the surface quality or the plastic composition, influence the optical properties of a measuring cuvette and therefore impair the precision of the optical analyses.
Modern analytical instruments can achieve a throughput of up to several hundred individual analyses per hour. Since one measuring cuvette is required for each individual analysis, the need for measuring cuvettes is correspondingly high. Therefore, in the analytical instruments, stock containers for measuring cuvettes are frequently provided which can take a relatively large number of measuring cuvettes in the form of a bulk good. The bulk good is typically delivered in plastic bags and is placed in the stock container of the analytical instrument by a user. Isolation mechanisms of various types ensure that one cuvette after another is removed from the stock container in order to then be available for a planned analysis. Such a stock container for cuvettes and a specific isolation mechanism are described, for example, in US-A1-2014/0295563.
It is problematic, however, that due to the storage and transport of the measuring cuvettes in the form of a bulk good, the cuvettes constantly rub against one another and thus the outer surface of individual cuvettes can be scratched. A scratched surface can however lead to undesired optical effects which, in particular in the case of scattered-light measurements, seriously impair the precision of an optical analysis.
This problem is solved in the prior art in different ways. One possibility is that the design of the cuvettes is adapted so that the region of the cuvette in which the optical measurement is carried out, i.e., the measuring window, is provided with a protecting raised frame so that at least the surface in the region of the measuring window is protected from scratching. Another possibility is that significantly more scratch resistant plastics such as cycloolefin copolymers are used instead of the polymethyl methacrylate and polystyrene plastics typically used.
The known solutions have the disadvantage, however, that they are relatively cost-intensive. Both the preparation of cuvettes with complicated architecture and the use of higher-value plastics increase the production costs in some cases by an order of magnitude.